Selector valve

ABSTRACT

A selector valve includes an annular body having a sealing surface having a plurality of inlet ports. The sealing head carries a seal member which is urged by a spring against the sealing surface. The sealing member has a sealing face comprising a central band and lateral areas above and below the central band. The lateral areas are reduced in size compared to the area of the central band to equalize wear of the sealing member.

This invention relates to a selector valve which may be used to controlflow between a plurality of inputs and a single output or between asingle input and a plurality of outputs. Although the invention will beprimarily described in relation to a sampling valve which can take fluidflowing from any of a plurality of inlets and direct it to a singleoutlet, it will be appreciated that the invention is equally applicableto a distributor valve arrangement acting in the opposite way and tocomparable structures and devices.

Typical known selector valves are describe in GB 995016D, U.S. Pat. No.4,191,213B, U.S. Pat. No. 5,046,522B, WO87/02428 and U.S. Pat. No.4,198,9641B.

In the prior known valves, for example the valve described inWO87/02428, and also in the known valve shown in FIGS. 1, 2 and 3 aknown selector valve 10 has a plurality of selectable ports 11 eachterminating at a sealing surface 12 which forms a path for and isslidingly engaged by a selector head 13 whose port 14 is surrounded by aseal member 15 urged against a surface 12 as by a spring 16. Referringnow to FIGS. 2 and 3 it will be seen that as the seal member 15traverses the mouths of the ports 11 in use there is a degree of wearover that central band 17 which engages the edges of the mouths of theports 11. After some use that central band 17 tends to become more wornthan the remainder of the seal member 15 and this wear is shown (in anexaggerated manner) as a central groove 18 in FIG. 3. It will beappreciated that the groove 18 effectively provides a leak path in thedirection of arrow 19.

It will be appreciated that comparable problems will arise in relationto similar selector valves, for example the selector valve described inspecification GB995016B wherein the selector head moves over a flatsurface rather than over a cylindrical surface. It is an object of theinvention to provide an improved selector valve.

The invention provides a selector valve having a plurality of selectableports terminating at mouths in a sealing surface which can be traversedby a selector head having a seal member which provides a seal between aselected port and a port of the selector head, the seal member having,considered in its direction of travel relative to the selectable ports acentral band which traverses those ports and lateral portions which donot traverse the ports, the areas of said lateral portions beingselected so that the wear which they undergo during their traversing ofthe sealing surface without contact with the selectable ports isgenerally equal to the rate of wear of the central band which traversesthe ports.

The invention also provides a selector valve having a plurality ofselectable ports terminating at mouths in a sealing surface which can betraversed by a selector head having a seal member which provides a sealbetween a selected port and a port of the selector head, the seal memberhaving, considered in its direction of travel relative to the selectableports a central band which traverses those ports and lateral portionswhich do not traverse the ports, wherein the area of the lateralportions of the seal member are smaller than the area of the centralband so as to wear at about the same rate as the central band.

The invention further provides a selector valve having a plurality ofselectable ports terminating at mouths in a sealing surface which can betraversed by a selector head having a seal member which provides a sealbetween a selected port and a port of the selector head, the seal memberhaving, considered in its direction of travel relative to the selectableports a central band which traverses those ports and lateral portionswhich do not traverse the ports, wherein the areas of the lateralportions of the sealing face of the seal member are reduced so as towear at about the same rate as the central band.

As it will be appreciated, the seal member has in the past generallybeen selected to be circular to uniformly surround the selected ports onthe selector surface. In carrying out the invention it is possible forthe circular seal member to be reduced in width in a directiontransverse to its path of travel by having flats formed on it.Alternatively an elliptical shape can be chosen having its longer axisin the direction of travel.

A further problem arises in relation to such selector valves in theprovision of a seal between a stem of the selector head and a staticpart of the valve. The selector head is usually mounted on the end of a(for example) "L" shaped length of ducting, one limb of which effectssimple pivoting about its axis and the other of which carries thesealing head at its end. The first limb, at its end, must be sealedrelative to static structure such as pipe work which will direct theselected input to, for example, analytic equipment.

It will be appreciated that for analytic equipment a high integrityrotary seal must be provided between the static parts and the rotatinglimb of the selector head. It is a further object of the invention toimprove such a selector valve by reducing the standards required for aneffective seal at that position.

The invention further provides a selector valve including a selectorhead comprising ducting having a first part which rotates about its axisand a second part which carries a selector seal at its free end, thefree end of the first part being sealed against non-rotating structureby an annular sealing ring, wherein a static tube extends into the firstpart of the ducting.

The provision of the static tube enables samples to be taken from flowwithin the ducting upstream of the sealing ring thus making any leak atthe sealing ring of lower significance. The portion of the ductingsurrounding the tube can lead to an exhaust vent via the sealing ring.The invention also provides a sampling arrangement including a selectorvalve as aforesaid and including a plurality of sample sources capableof causing a given flow rate in the selector head conduit and incombination with destination equipment having a flow requirement lessthan the flow rate in the selector head ducting, excess flow in theducting being allowed to pass outside the selector tube passed throughthe annular seal between the end of the ducting and static parts and bevented to waste.

The destination equipment can be analytic equipment such as a gaschromatograph.

The invention will be described further, by way of example, withreference to the accompany drawings wherein:

FIG. 1 is a plan view of a known selector valve;

FIG. 2 is an end elevation of a seal member of a selector head of thevalve of FIG. 1;

FIG. 3 is a perspective view of the seal member;

FIG. 4 is a cross-sectional view of the selector of FIG. 1 modified inaccordance with the invention;

FIG. 5 is a view similar to FIG. 2 but showing the invention;

FIG. 5a is an enlarged view of FIG. 5;

FIG. 5b is a perspective view of FIG. 5;

FIG. 6 is a view similar to FIG. 5 but showing a variation;

FIG. 7 is a cross-sectional view of a selector valve in accordance withthe invention

FIG. 8 is a view similar to FIG. 7 but showing the selector valve ofFIG. 7 modified in accordance with a second feature of the presentinvention;

FIG. 9 shows a modification to the selector valves shown in FIGS. 5, 6and 7; and

FIG. 10 shows to an enlarged scale a detail of the modification shown inFIG. 9; and

FIG. 11 shows a modification to the arrangements shown in FIGS. 7 and 8.

Referring now to FIGS. 4 and 5 it will be seen that instead of thearrangement of FIGS. 1, 2 and 3 (which has already been described) apreferred valve of the invention has an annular body 21 providing acircular sealing surface 22 into which open the mouths 23 and aplurality of selectable inlet ports 24. A sealing head 25 includes onelimb 26 of selector ducting 27 whose other limb 28 is disposed on androtatable about an axis of the valve. The selector head 25 carries aseal member 29 which is urged by a spring 30 against surface 22 and hasa sealing face which is shown in FIG. 5. As best seen in FIG. 5a thesealing face of the seal member 29 has a central band 31 which, in use,traverses the mouths 23. Lateral areas above and below the band 31 areindicated at 32 and 33.

As best seen in FIG. 5a the lateral areas 32 and 33 are reduced in sizecompared to the area of the band 31. The reduction in size is such thatthe area of the band 31 (ignoring the central aperture communicatingwith the ducting 26) is greater than the areas 32 and 33. This reductionin the size of the areas 32 and 33 means that the contact pressureimposes greater wear on the areas 32 and 33 during the sliding movementwith the surface 22.

Thus, in use the central band 31 and the areas 32 and 33 wear in unisonand the groove illustrated at 18 in FIG. 3 does not develop. Or, if itdoes, only develops after a prolonged period of use at which stage theseal can be replaced.

The valve 20 of FIG. 4 is more completely described in FIG. 7 and itwill be seen that the sealing head 25 forms part of a distributor whoseporting has a limb 28 sealed by annular seal 34 to part of a housing 35to which is connected pipe work 36 which can lead to destinationequipment, for example analytic equipment such as a gas chromatograph.The selector head is rotated by means of a shaft 37 and non-selectedports 11 vent to the interior 38 and exit via exhaust port 39. It willbe appreciated that the interior of the housing 35 illustrated at 40will be filled with un-selected fluid streams and therefor the integritybetween the ducting 28 and that interior must be maintained quite highlyby the seal 34. Any leakage through the seal 34 could cause entry offluid into the sample.

FIG. 8 illustrates how, in accordance with a second feature of theinvention the danger of leakage at the seal 34 can be significantlyreduced. Here, a sampling tube 41 passes fixedly through the pipe work36 and enters telescopically into the ducting 28. The tube 41 lies onthe axis of rotation of the selector head and therefore is a staticitem. The free end 42 is well upstream (considered in the direction offlow of sampled product) and therefore the product to be sampled entersvia the open ended tube 42 passes down tube 41 and passes to its usedestination. Excess flow carries on in the annular space 43 to exhaust.It will be appreciated that any leakage at the seal 34 does not affectthe sample selected because it will be virtually impossible for anycontaminant to pass, to the left in FIG. 8, from the seal 34 towards theinlet 42 against the flow in the space 43. This allows the seal 34 to bean item of less expensive and less critical construction and itsinspection and maintenance, although necessary, can be reduced infrequency and therefore in cost.

Referring to FIGS. 9 and 10 there is shown a modification which can beapplied to the selector valves shown in FIGS. 4, 5, 6, 7 and 8.Components similar to those in the previous figures have been accordedidentical reference numbers. The spring (30) seats at one end against ashoulder (44) provided on the limb (26). The opposite end of the spring(30) seats against an inner sealing ferrule (45) which is mounted on thelimb (26) and positioned within a recess (46) within the seal member(29).

The function of the sealing ferrule (45) is to prevent leakage along thepath formed between the external diameter of the limb (26) and theinternal diameter of the sealing member (29). This leakage increaseswith temperature due to the differential thermal expansion rates of theseal member which is formed from PTFE and the stainless steel limb (26).

The load exerted by the spring (30) acts on the sealing member (29) viathe sealing ferrule (45). This spring loading forces the lip (45A) ofthe ferrule into intimiate contact with the sealing member (29) and thelimb (26) so forming a sliding seal.

The sealing takes place at a point very close to the open mouth of theport face and thus minimises accumulation of sample material trapped inthe path mentioned above.

Referring to FIG. 11, the sealing ferrule (45) is shown being urged intocontact with the sealing member (29) by the spring (30) which bears atone end against a seating (47) provided on the shaft (37) and the limb(26) extends through a duct (48) formed in the shaft (37).

The invention is not limited to the precise details of the foregoing andvariations can be made thereto. Clearly the invention (except for theoptional feature of the static sampling tube 41) is applicable to valveswherein there is either distribution or sampling and wherein theselector head moves over a flat, conical or other surface into whichextend a number of mouths of selectable ports.

Many other variations are possible within the scope of the invention.

I claim:
 1. A selector valve comprising a plurality of selectable portsterminating at mouths in a sealing surface; a selector head thattraverses the sealing surface, the selector head having a seal memberwhich provides a seal between a selected port and a port of the selectorhead, the seal member being in constant contact with the sealing surfaceand having, considered in its direction of travel relative to theselectable ports, a central band which traverses the selectable portsand lateral portions which do not traverse the selectable ports, a widthof the central band being equal to a width of the selected port and alength of the central band being greater than a length of the lateralportions, and the area of the lateral portions being selected so thatthe wear which the lateral portions undergo during their traversing ofthe sealing surface without contact with the selectable ports isgenerally equal to the rate of wear of the central band which traversesthe selectable ports.
 2. A selector valve as claimed in claim 1, whereinthe areas of the lateral portions of the seal member are smaller thanthe area of the central band so as to wear at about the same rate as thecentral band.
 3. A selector valve as claimed in claim 1, wherein theseal member has a truncated circular surface providing the seal betweenthe selected port and the port of the selector head, the truncatedcircular surface being defined by a circular area reduced in width in adirection transverse to its path of travel by having flats along cordsof the circular area, the cords being parallel to the path of travel. 4.A selector valve as claimed in claim 1, wherein the seal number has asurface providing the seal between the selected port and the port of theselector head, the surface being of generally elliptical cross sectionhaving its longer axis in the direction of travel.
 5. A selector valveas claimed in claim 1, wherein the selector head further comprisesducting having a first part which rotates about its axis and a secondpart which carries the seal member at its free end, a free end of thefirst part being sealed against a non-rotating structure by an annularsealing ring, wherein a static tube extends into the first part of theducting.
 6. A selector valve as claimed in claim 5, wherein a portion ofthe ducting surrounding the static tube leads to an exhaust vent via thesealing ring.
 7. A selector valve as claimed in claim 6, furthercomprising a plurality of sample sources capable of causing a given flowrate in the selector head ducting in combination with destinationequipment having a flow requirement less than the flow rate in theselector head ducting, excess flow in the ducting being allowed to passoutside the static tube, through the annular seal, between the end ofthe ducting and the non-rotating structure and vented to waste.
 8. Aselector valve as claimed in claim 7, wherein the destination equipmentis analytic equipment.
 9. A selector valve as claimed in claim 8,wherein the analytic equipment is a gas chromatograph.
 10. A selectorvalve, comprising,a plurality of selectable ports terminating at mouthsin a sealing surface; a selector head that traverses the sealingsurface, the selector head having a seal member which provides a sealbetween a selected port and a port of the selector head, the seal memberbeing in constant contact with the sealing surface and having,considered in its direction of travel relative to the selectable ports,a central band which traverses the selectable ports and lateral portionswhich do not traverse the selectable ports, a width of the central bandbeing equal to a width of the selected port and a length of the centralband being greater than a length of the lateral portions, and the areaof the lateral portions being selected so that the wear which thelateral portions undergo during their traversing of the sealing surfacewithout contact with the selectable ports is generally equal to the rateof wear of the central band which traverses the selectable ports; and aforce applying member that applies a force to the seal member such thatthe seal member is maintained in constant contact with the sealingsurface.
 11. A selector valve as claimed in claim 10, wherein the areasof the lateral portions of the seal member are smaller than the area ofthe central band so as to wear at about the same rate as the centralband.
 12. A selector valve as claimed in claim 10, wherein the sealmember has a truncated circular surface providing the seal between theselected port and the port of the selector head, the truncated circularsurface being defined by a circular area reduced in width in a directiontransverse to its path of travel by having flats along cords of thecircular area, the cords being parallel to the path of travel.
 13. Aselector valve as claimed in claim 10, wherein the seal member has asurface providing the seal between the selected port and the port of theselector head, the surface being of generally elliptical cross sectionhaving its longer axis in the direction of travel.
 14. A selector valveas claimed in claim 10, wherein the selector head further comprisesducting having a first part which rotates about its axis and a secondpart which carries the seal member at its free end, a free end of thefirst part being sealed against a non-rotating structure by an annularsealing ring, wherein a static tube extends into the first part of theducting.
 15. A selector valve as claimed in claim 14, wherein a portionof the ducting surrounding the static tube leads to an exhaust vent viathe sealing ring.
 16. A selector valve as claimed in claim 15, furthercomprising a plurality of sample sources capable of causing a given flowrate in the selector head ducting in combination with destinationequipment having a flow requirement less than the flow rate in theselector head ducting, excess flow in the ducting being allowed to passoutside the static tube, through the annular seal, between the end ofthe ducting and the non-rotating structure and vented to waste.
 17. Aselector valve as claimed in claim 16, wherein the destination equipmentis analytic equipment.
 18. A selector valve as claimed in claim 17,wherein the analytic equipment is a gas chromatograph.
 19. A selectorvalve as claimed in claim 10, wherein the force applying member is aspring.